This invention relates to liquid applicators including writing instruments such as ball-point pens and paint markers.
In general, the liquid applicators including writing instruments are each provided with a tubular casing for containing liquid to be applied and a hollow lead portion mounted on a lead end of the casing. The easing and the lead portion are coupled with each other by spirally engaging a thread formed on the casing with a thread formed on the lead portion. However, if the spiral engagement of these threads loosens while the liquid applicator is in use, the liquid contained in the casing may leak out and stain documents, clothes, and bodies of users. Particularly, recent years, the toxicity of the liquid has been raised as problem. In this respect, it has become important to prevent leakage of the liquid to be applied.
The following are known as means for preventing loosening of the spiral engagement described above.
(a) A hollow lead portion is provided with an elastic piece having a projected portion, and a tubular casing is provided with a groove-like engaging portion which is spirally engageable with the projected portion of the lead portion. By engaging the projected portion with the groove-like engaging portion, the spiral engagement of the threads becomes resistive to the external force, and therefore the rotation of the lead portion relative to the casing can be restricted (Japanese Unexamined Utility Model Publication No. 57-13284).
(b) Either the casing or the lead portion is provided with a cylindrical portion having a projected portion which serves as a stopper, and the other is provided with an engaging portion which is stopped by the projected portion. Further, in adjacent to the engaging portion is provided a tapered portion which becomes struck against the projected portion, thereby causing the threads to become meshed with each other. In this way, the loosening of this spiral engagement of the two threads can be restricted (Japanese Unexamined Utility Model Publication No. 60-48471).
The liquid applicators disclosed in the above publications are both capable of restricting the loosening of spiral engagement of the casing and the lead portion. However, even in these liquid applicators, the loosening of the spiral engagement still remains possible. Accordingly, there still exists a demand for liquid applicators capable of preventing the loosening of the spiral engagement more reliably.